The first documentation of this building dates back to 956, during Sancho I of Leon's reign. This King's intentions were to build a temple to accommodate Pelayo's relics. He was a boy that was martyred in Cordoba in 925, whose fame extended all over the European Christianity. He made the opportune paperwork together with the Court of Al-Andalus, where he had been a hostage, to transfer the body. He could not make it because he was killed. His sister Elvira Ramírez (nun and regent of her nephew Ramiro III) together with Teresa Ansúrez, Queen Mother, widow of Sancho I, achieved this project's fulfilment so the rests of Pelayo were transferred from Cordoba to Leon. Elvira Ramírez was a nun in San Salvador de Palat del Rey, a monastery founded by her father, the King Ramiro II, built next to his palace, which was exclusively for royal women. Elvira and her community moved to the new temple of San Pelayo, which was just built to receive the martyr's relics. Life in this monastic community lasted only 20 years in this place, under the legal denomination of "Infantado de San Pelayo", a medieval institution from Leon for the single Infantas that held the title of abbess or "domina" (Lady). During Bermudo II's reign, in particular in 988, Leon suffered the attacks and devastations of Almanzor. The little church of San Pelayo was destroyed. By then, the first abbess Elvira had already died. Teresa Ansúrez, the widow queen, succeeded her. When she knew about the imminent razias in Almanzor, she took Pelayo's body to the city of Oviedo to preserve the relics. Alfonso V, Leon's King between 999 and 1028, ordered to rebuild many buildings, among which we find the monastery of San Pelayo, after Leon's devastation. The community of nuns and Canons Regular of St. Augustine was reorganized again, each of them under the command of the new abbess Teresa, Alfonso V's sister. Sancha of Leon, daughter of Alfonso V, was abbess at the monastery of San Pelayo since very young age. She was monarch of Leon together with her husband Fernando since 1037. Sancha notably influenced on the King Fernando to carry out the construction in stone of the church of San Juan Bautista, which was attached to the monastery. The project took place but it was not a big temple opened to the believers but a little palatial church for its patrons, Fernando and Sancha, that lived in their palace located next to the double monastery. To expand the church and according to that time's habits, it was necessary to count on important relics. So they brought from Seville San Isidoro's body in 1062. They also brought from the monastery of Arlanza the relics of San Vicente of Avila that were saved there due to the razias of Almanzor. They counted on the jaw that it was said to be of San Juan Bautista too. On the 21st of December 1063, this new church was consecrated and was dedicated to San Isidoro. The Kings maintained a total protection for the temple. They provided it of notable relics and goldsmithing objects; they enriched the church with treasures and the monastery with a huge patrimony. The infanta Urraca Fernández de Zamora, who was single, was also the owner of the Infantado de San Pelayo. She possessed the estate of the kingdom's monasteries whose head was the one of San Isidoro de Leon. When her mother Sancha died in 1067, she inherited the financial support and maintenance of the temple. She ordered to make many extension works but she did not see them finished. On the contrary, Alfonso VII and his sister, Sancha Raimúndez, also Lady of the Infantado completed the works. Their parents were Urraca and Raimundo de Borgoña. They completed the works started by their great-aunt Urraca and solemnly consecrated the church on the 6th of March 1149. The Infanta Sancha restored the monastic life and professed herself in the monastery. She ordered the monastery to depend on the Canons Regular of St. Augustine in 1147 and moved the community of nuns out of Leon. The infanta ordered to construct the buildings destined to the canons. Shortly after, the monastery became an abbey. Ferdinand II, King between 1157 and 188 and Alfonso VII's second child, achieved through the pope Alexandre III that the monastery and its church became an abbey with a series of privileges among which there was the exemption of every episcopal jurisdiction. In addition to the great reforms made during the Romantic period, the architectonic complex of San Isidoro suffered partial works, modifications ordered, in some cases, by different people for their glory and convenience and for the general improvement, in others. Finally, the 19th century was the worst of its history. In the first years, it was occupied by the French troops and was later plundered. The rooms and chapels turned into quarters, a straw loft and stables. When they had to retire, they burnt the church. Some years later, in 1835, Mendizábal's disentailment took place and, as a consequence, there were new loots and plunderings. The community was abolished but it was reestablished on the 25th of May 1851 by the concordat and the bull Inter Plurima of the pope Pius IX. The restoration started in 1894. In 1956, after the community's deterioration and the limited presence of the monastery's members, the bishop of Leon transformed it into "Cabildo Secular de San Isidoro" (Secular Canonry of San Isidoro).